This invention relates generally to inductor structures and manufacturing methods and more particularly to spiral inductors adapted for use in monolithic microwave integrated circuits.
As is known in the art, active devices, such as transistors, and passive devices, such as resistors, capacitors and inductors, have been formed on a common single crystal substrate, such as gallium arsenide (GaAs), as a microwave monolithic integrated circuit . One technique used to form the inductor has been to: first form the active devices in the gallium arsenide, deposit a passivation layer of silicon nitride over the processed gallium arsenide, and pattern a layer of photoresist deposited over the silicon nitride layer with a spiral shaped window formed therein. Next, a sequence of titanium followed by gold is deposited over the photoresist layer and through the spiral shaped window onto the exposed portions of the silicon nitride. The photoresist layer is then removed, i.e., "lifted-off", leaving a spiral shaped inductor on the silicon nitride passivation layer.
While such technique has been useful in many application, the inductor has a relatively low impedance resulting in a relatively narrow bandwidth device.